DVB-H technology derives from the standard DVB-T (Digital Video Broadcast, Terrestrial) with which it is largely compatible while having particular characteristics depending essentially on the features of the mobile reception equipments.
A known problem with DVB-H mobile equipment is the limited capacity of the batteries. In fact, the compatibility with the DVB-T standard requires demodulation and decoding mechanisms at wide band and high data throughput (up to 10 Mbit/s per channel) leading to a high energy consumption of the concerned electronic circuits. The solution adopted to reduce consumption is the transmission of the stream in bursts rather than continuously. The mobile receiver equipment is thus only enabled periodically to receive the bursts and is in stand-by mode during the interruptions. This mode, specific to DVB-H, thus allows a reduction of the consumption of the mobile equipment by a factor ten or more.
In general, the broadcasted stream comprises several multiplexed services such as for example an audio/video content, files or software applications to be downloaded. In the DVB-T mode, the whole stream is decoded before being able to access a selected service. The energy saved by the DVB-H mode is based on the fact that only the parts of the stream containing the data of a selected service are processed, which requires a suitable reorganization of the stream. The multiplexing of services is then carried out according to a time slicing. The data of a particular service is not transmitted in a continuous way but in compact periodic bursts with interruptions between the bursts.
In the case of conditional access digital pay television, the data stream comprises the encrypted audio/video content, control messages and management messages. The control messages ECM (Entitlement Control Message) contain control words for decrypting the audio/video content. In the DVB-T mode where the stream is transmitted in a continuous way, decryption is carried out by a decoder in direct mode at reception of data or in deferred mode after storage of all or part of the stream. The control messages are decrypted for allowing the extraction of the control words used to decrypt the broadcasted content. In order to synchronize the control messages with the broadcasted or recorded content, different solutions have been developed among which we can mention:                The document US2003152364 proposing the introduction of several control words in a control message ECM. Such a message contains the current control word to decrypt the data block in process, the control words preceding and following this current word for decrypting a recorded stream and this in the rewind or fast forward modes of a digital audio/video recorder.        The document EP1447983 concerns the creation of a correspondence table between recorded parts of the stream and control messages accompanying the recorded parts of the stream.        The document EP0583202 describing the transmission with each program of a control message pertaining to this program with a certain frequency and the control messages pertaining to other programs with a lower frequency. The control message of the selected program is used to decrypt it in direct mode and the other control messages are stored to be able to proceed quickly to the decryption of another program to be selected afterwards.        
In DVB-H technology, the stream comprises a plurality of services transmitted by successive bursts containing the encrypted content (digital audio/video programs, files or software applications, etc.) and the control messages necessary for the decryption of the content. At passing from one service to another or during the interruptions of stream reception, it is possible to receive the bursts of content without receiving the corresponding control messages. This problem is due to the fact that the bursts of control messages are not synchronized with those of the content. Each burst is transmitted in the form of independent IP packages (Internet Protocol). When the receiver is locked on a given channel, this interval is not important as the control words contained in the control messages relate to blocks transmitted subsequently with respect to the current blocks. For example, in the case of successive service or channel changes (zapping), the bursts of content can be received without being decrypted by a control word because of the non-reception of the corresponding control messages due to the lack of synchronization of the “content” and “control messages” services.
The solutions of the prior art according to the aforementioned examples do not apply in the case in which the stream is made up of bursts corresponding to independent services. As the mobile equipment is only activated for selected services, it cannot receive data from other services as in the case of a continuous stream and of a receiver activated to receive all the services of the stream. In fact, in DVB-T mode, the stream is decoded in its entirety for accessing a service, thus the control messages can be received constantly even if the user switches from one service to another.
In the document of the ETSI TR 102 377 “DVB-H Implementation Guidelines” standards, the receiving mobile equipment must receive the control messages ECM before the bursts. The proposed solution consists of activating the receiver before reception of a burst in order to wait the arrival of ECM messages. These messages are transmitted in continuous mode independently of the bursts stream and the minimum time interval between the messages has to be lower as the duration of a burst.